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Costello 

Solar Demonstrating 
Globe 


By 

Garrett P. Serviss 



Manufactured by 

Weber Costello Company 

CHICAGO HEIGHTS, ILLINOIS 








Globes 

Hyloplate Blackboards 
Erasers—Wall Maps 

And Other 

SCHOOL SUPPLY 

SPECIALTIES 


h 



KNOWN WHEREVER THERE ARE SCHOOLS 


Copyrighted 1922 


WEBER COSTELLO COMPANY 

CHICAGO HEIGHTS ILLINOIS 

MANUFACTURERS FOR THE TRADE ONLY 







© Cl A6S2642 





AUG i 8 '22 




INDEX 


Illustration—Costello Solar Demonstrating Globe, Index to Parts. 

Introduction . 

How to Use the Costello Solar Demonstrating Globe. 

Illustration-The Earth’s Position in Relation to the Sun. 

Fundamental Relations of Sun and Earth. 

The Sun’s Daily Motion: 

Cause of Day and Night. 

The Cap of Day... 

The Cap of Night... 

Angular Rate of the Earth’s Rotation.—. 

The Sun’s Yearly Motion-The Seasons. 

Why Summer Is Hot and Winter Cold... 

The Sun’s Two Motions Combined.. 

The Time of Equal Days and Nights.-. 

Unequal Days and Nights. 

Wonderful Phenomena at the Poles. 

Day and Night Inside the Polar Circles. 

Day and Night Between the Equator and the Polar Circles. 

The Times of Sunrise and Sunset: 

At the Equinoxes. 

At the Solstices. 

Refraction . 

Twilight ... 

The following subjects are included in this Manual because 
of their relation to the preceeding matter and their educa¬ 
tional value. The Costello Solar Demonstrating Globe is 
not, however, suited to use in conjunction therewith: 

Precession of the Equinoxes.-. 4 — 

The Sun ...-. ----- 4 . 

The Earth .*. . .. . . 

The Magnetic Poles.*. . . 444 ' 4 * 4 . 

The Equation of Time.-.....-. . . 

Inequalities of Forenoon and Afternoon. 

Different Kinds of Day and of Year. 

The Standard Time Zones.-. 

Illustration—Standard Time Zones. 

1 


II 

HI 

V 

1 

2 

3 

3 

4 

5 

6 

9 

10 

12 

13 

14 

15 

16 

19 

20 

22 

23 

25 

27 

28 

29 

30 

33 

33 

36 

37 
































COSTELLO SOLAR DEMON¬ 
STRATING GLOBE 

Copyrighted 1922 

Patent Applied For 



A —Globe Base. 

B—Inclination Plate. 

C—Sun. 

D—Day and Night Circle. 
E—Quadrant. 

F—Globe Ball. 


LIST OF PARTS 

G—Thumb Nut (under base). 

H—Nut for Quadrant. 

I—Semi Horizon. 

J—Semi Horizon Support. 

K—Set Screw for Day and Night Circle. 


To my mind this is as admirable a means of teaching astron¬ 
omy as could be imagined. The globe ought to go into every 
school, carrying mental daylight with it .... It is not only an 
aid to instruction—it is itself the chief instructor. 








COSTELLO SOLAR DEMONSTRATING GLOBE 


INTRODUCTION 
Description of the Apparatus 

The Costello Solar Demonstrating Globe is an apparatus designed to 
show, by visual demonstration, the effects of the relations between the 
sun and the earth upon the distribution of light and heat, of day and 
night, and of the changing conditions of the seasons. What the almanac 
tells, without explaining the mathematical calculations on which its pre¬ 
dictions are based, this apparatus shows to the eye without the necessity 
of any calculations. Occasionally a little of the very simplest arithmetic 
is all that need be used. 

The apparatus consists of an ordinary globe of the earth, “F,” 
mounted within a vertical bronze circle “D” which represents the divid¬ 
ing line between day and night. This circle is called the “Day and Night 
Circle.” 

The earth globe is mounted within this circle with its polar axis in¬ 
clined 2 3 1/2 degrees from a perpendicular. This inclination corresponds 
to that of the axis of the earth with respect to the plane of the orbit in 
which it travels around the sun, called also the plane of the ecliptic. 

The Day and Night Circle is so mounted that it can be freely 
swung round a vertical axis into any desired position. 

Independently, the earth globe can be rotated on its axis inside the 
Day and Night Circle, the motion of neither interfering with that of the 
other, and both motions may be performed at the same time. 

Projecting out from the Day and Night Circle on one side are two 
curved metal supports, one, “I,” fixed horizontally, in the plane of the 
ecliptic, while the other, “J,” is vertical. These sustain at their point of 
junction, exactly over the center of the Day and Night Circle, and at a 
distance from it equal to the radius of the Circle, a small bronze ball, 
“C,” which represents the sun. A projecting point on the inner side of 
this sun-ball is called the “Sun’s Central Ray,” its purpose being to show 
over what point on the earth the center of the sun is vertical at any time. 
The sun-ball of course moves with the Day and Night Circle to which it is 
attached by the supports, remaining at a distance of 90 degrees from 
that circle on all sides. 

On the “sun” side of the Day and Night Circle, and at the bottom, 
is a small thumb-screw, “K,” by means of which the Circle, and with it 
the sun, can, when desired, be fixed firmly in position, while the earth 
globe is rotated within. 

Attached by another small thumb-screw, “H,” to the north pole, 
and curving down over the globe, is a graduated copper indicator, “E,” 
called a “Quadrant,” its length being equal to a quarter of a circle. 
When the screw is loosened the Quadrant may be swung in either direc¬ 
tion over the globe, and then fixed in any position. When the Quadrant 
is thus fixed by tightening the screw at the north pole, and the earth is 
rotated, the movement of the point of the Quadrant along the equator 
of the globe indicates the number of degrees turned by the globe, and 


III 




COSTELLO SOLAR DEMONSTRATING GLOBE 


this is the principal use of the Quadrant, although it may also be em¬ 
ployed to measure the latitude of places on the globe. Its uses are indi¬ 
cated in the pages that follow. 

When it is desired to use the Globe simply for geographical pur¬ 
poses, the sun-ball may be swung around to the side opposite the ob¬ 
server and fixed there by means of the thumb-screw at the bottom. The 
north pole will then be under the 90th degree of latitude near the top of 
the circle. The meridians, or circles of longitude, on the globe are drawn 
1 5 degrees apart, whereby they serve as hour-circles in reckoning stand¬ 
ard time, which begins at the Prime meridian, or meridian of Greenwich, 
and follows the sun around westward, so that it is noon on the 1 5 th de¬ 
gree west one hour after it was noon at Greenwich; noon on the 30th 
degree west two hours after it was noon at Greenwich, and so on. 

Half way around the globe from the Greenwich meridian, i. e. 1 80 
degrees from Greenwich counting either west or east, is the ‘Date Line” 
which runs through the middle of the Pacific ocean, and on which each 
new calendar day is assumed to begin. When it is noon at Greenwich, 
or anywhere on its meridian, it is midnight on the Date-Line. Since by 
the civil calendar every day begins at midnight, evidently each succes¬ 
sive day may be said to have its birth on the Date Line, at the moment 
when its immediate predecessor is 12 hours old at Greenwich. (We are 
here using the word “day” in its astronomical significance, as the interval 
of time occupied by a single ro¬ 
tation of the earth on its axis— 

24 hours). When a ship crosses 
the Date Line sailing eastward 
it goes back a day in its reckon¬ 
ing, while if it crosses sailing 
westward it goes forward a day. 

For instance if the ship is going 
from California to Japan and 
reaches the Date Line at 1 0 A. 

M. on a Monday, it will, as soon 
as it is over the Line, skip to 1 0 
A. M. Tuesday. But if the ship 
is sailing from Japan to Califor¬ 
nia it will go back from 1 0 A. 

M. Tuesday to 1 0 A. M., Mon¬ 
day. 

Although upon the whole the 
Date Line follows the 180th 
meridian, yet, as marked on the 
Globe it shows a number of zig¬ 
zags. These were made to in¬ 
clude certain islands on one side 
or the other of the Line, whose 
local dates depend upon whether 
they were discovered by ex¬ 
plorers coming from the east or 



IV 




COSTELLO SOLAR DEMONSTRATING GLOBE 


from the west. But in the open ocean ship captains go by the Date 
Line only. 

The parallels of latitude run east-and-west around the Globe paral¬ 
lel with the equator, and are for convenience marked at intervals of 1 0 
degrees. The pupil may be shown how, while the angular velocity of 
the earth s rotation is the same from the equator to the poles, the linear 
velocity, i. e. the number of miles moved per hour, is greatest at the 
equator and least near the poles. Standing on the pole itself a person 
would simply turn round and round on a vertical axis once every 24 
hours. 

In adjusting the apparatus for use in the demonstrations described 
in this manual the sun-ball should be placed on the side of the Globe 
facing you. The simplest way to shift the position of the sun and of the 
Day and Night Circle is to take hold of the vertical support just under 
the sun-ball and move it to the right or left as desired. (See cut). To 
place the sun over a given date on the ecliptic circle, it is easiest to set 
the Globe before you with the north pole exactly under the Day and 
Night Circle and inclining to the right. The North Pole will then point 
to the 43rd degree N. Lat. on the Day and Night Circle. Then the 
ecliptic will lie horizontally, parallel with the horizontal support of the 
sun-ball, and, without rotating the globe, you can push the sun around 
to right or left until its Central Ray is exactly over any desired date. 
Fix it there with the thumb-screw, and then you can rotate the globe 
at will. 

HOW TO USE THE COSTELLO SOLAR DEMONSTRATING GLOBE 

It may be confidently be affirmed that a few days, or at most a week 
or two, of experience with this simple apparatus, will afford a better com¬ 
prehension and mastery of the important and very practical field of 
knowledge that lies on the border between geography and astronomy, 
involving the relations between the earth as an inhabited planet and the 
sun as the source of the light and heat which make that planet habitable, 
than can be obtained by months of study of text-books, or of blackboard 
demonstrations. The pupil sees the phenomena virtually taking place 
before him, while he listens to the teacher s explanation—and in many 
cases the explanation stands out for itself, or a very brief examination 
reveals it, thus giving to the pupil that most inspiring sense of seeing and 
discovering with his own eyes. 

And for self-instruction at home nothing could be more valuable 
than the Costello apparatus, while the need of something of the kind is 
emphasized by the fact that the majority of even educated people go 
through life without ever clearly understanding the simple facts on which 
an almanac is based. The Costello Globe makes them perfectly plain. 

What follows is intended as a suggestive guide both for teachers 
and for those who teach themselves. We here recall the principal 
astronomical and geographical data concerned, and point out both how 
to use the apparatus, and how it may be used in such a way as to re¬ 
double the interest of both pupil and teacher. 


v 





Position of Earth in relation to Sun, March 21st (upper), June 22nd (left), Sept. 23rd (lower) 

and Dec. 22nd (right). 

See pages 23 describing the procession of the equinoxes. 










COSTELLO SOLAR DEMONSTRATING GLOBE 


FUNDAMENTAL RELATIONS OF SUN AND EARTH 

The continually changing phenomena of the seasons and of day and 
night are due to three great causes, the first two of which are apparent 
motions of the sun produced by two real motions of the earth, while the 
third cause is a permanent inclination of the axis of the earth, which may 
be likened to the peg of a top that does not stand upright while the 
top spins. 

The two real motions are: (1), The rotation of the earth, once 
every 24 hours, on an axis running north and south through its center, 
from pole to pole—which is the cause of the succession of day and night; 
and (2), The revolution of the earth around the sun once every year in a 
path called its orbit,—which is one of the causes of the change of sea¬ 
sons; the other cause being the inclination of the axis already referred to. 

The two apparent motions are: (1), The daily movement of the 
sun through the sky, from its rising to its setting point, or from east to 
west, which is a relativity effect due to the earth s daily rotation on its 
axis from west to east: (2), The yearly passage of the sun around the 
sky, against the background of the stars, which is also a relativity effect 
due to the earth’s yearly revolution around the sun, although, in this case, 
the sun appears to move around in the same direction as that of the 
earth’s motion, i. e. from west to east. To explain this difference let a 
boy stand in the middle of a circular race-track while another boy runs 
around the track. To the runner the motionless boy will appear to be 
moving around against the background in the same direction in which he 
is running, thus, as it were, keeping ahead of him. But if the runner 
stops and simply rotates on his heels, then the other boy will appear to 
be revolving around him in a direction opposite to his own rotation. 

The third thing to consider is the inclination of the earth’s axis of 
rotation, which, as we have said, is one of the causes of the change of 
seasons. Now, to what is the earth’s axis inclined? To the plane in 
which the earth revolves around the sun, which is called both the plane 
of the earth’s orbit and the plane of the ecliptic. Instead of spinning 
like a top with its peg standing straight, the rotating earth as it revolves 
around the sun keeps its axis always leaning one way, at an angle of 23^2 
degrees from the perpendicular. 


2 



COSTELLO SOLAR DEMONSTRATING GLOBE 


THE SUN’S DAILY MOTION—CAUSE OF DAY AND NIGHT 



For convenience we shall hereafter speak of the apparent motions 
of the sun as if they were real, because the eye is completely deceived 
by them. 

Let us now place the Costello Solar Demonstrating Globe before us 
with the sun on the side toward us, both poles under the Day and Night 
Circle and the north pole in¬ 
clined toward the right. Observe 
that the earth s equator is repre¬ 
sented by a circle of black and 
yellow checks running around 
the globe half way between the 
poles. There is another circle 
made up of black and red 
checks which represents the ec¬ 
liptic. This runs directly under 
the sun and crosses the equator 
at two diametically opposite 
points on the globe. The two 
circles are inclined to one an¬ 
other at an angle of 23J/2 de¬ 
grees. We shall deal with this 
later, but for the present we are 
especially concerned with the 
equator. 

Bring the point where the 
equator, the ecliptic, and the 
north-and-south meridian, mark¬ 
ed “Meridian of Greenwich,” 
all cross together, to the center 
of the globe as it stands before 
you; then move the sun until its 
central ray is exactly over that 
point, and fix it there by tight- 
ing the screw “K“ at the front of the Day and Night Circle. Then 
rotate the earth from west to east, i. e. from left to right. That is the 
way you would actually see it turning if you were thousands of miles up 
in the sky with your head to the north and your feet to the south, and 
looking down upon the earth. 


The Cap of Day 

Now, observe how as the earth turns from west to east the little 
bronze ball representing the sun seems to speed from east to west across 
the oceans and continents, keeping always over the equator. Notice that 
in its westward motion over the earth the sun carries a hemispherical cap 
of daylight with it, which fits over the half of the globe that is turned 


3 




COSTELLO SOLAR DEMONSTRATING GLOBE 


toward the sun, reaching to the Day and Night Circle all around, but not 
passing beyond it. Behind that circle, on the side away from the sun, 
the surface of the earth is buried in night. The sun is like a center button 
on the top of the cap of day. 

The western (left hand) rim of the Day and Night Circle shows 
where the sunrise line lies upon the earth, and the eastern (right-hand) 
rim marks the sunset line. The Circle thus marks the boundary between 
daylight and darkness. Every point on that circle is always 90 degrees 
from the sun, but the circle is constantly shifting its position westward 
over the surface of the globe as the earth turns on its axis. On the west¬ 
ern verge the lands and seas are continually coming into the sunlight, or 
we may say that there the dawn is racing ahead of the sun, keeping 90 
degrees in advance of it. 

Right under the sun it is noon, but it is also noon all along a straight 
north-and-south line, or meridian, drawn from pole to pole through the 
sun s central ray, and the noon line, like the sunrise line, flies westward 
over the earth just as fast as the sun. Go round the earth keeping up 
with that line and you would always be in the noon sunshine. 

Note that all places on the earth lying west of the noon line are in 
the forenoon, and all places lying east of that line are in the afternoon. 

The Cap of Night 

Then look at the eastern (right-hand) edge of the Day and Night 
Circle. There darkness is swallowing up daylight. It is the border of 
the earth’s revolving night cap. The “trailing garments of the night” 
follow the sunshine westward over the earth. It is both interesting and 
very instructive to watch first Europe and Africa, then the Atlantic ocean, 
then the Americas, then the broad Pacific, then Australia and Asia pass 
under the Day and Night Circle on the right, thus going behind the cur¬ 
tain of darkness, while the opposite side of the globe, they issue again 
into daylight, following one another in the same order. Only from such 
a life-like presentation of the phenomenon can a clear idea be obtained 
of the alternation of day and night on different parts of the earth. 

Observe, too, that just as the noon line lies straight north and 
south, i. e. from pole to pole, on the earth’s surface, and at right angles 
to the equator, so if you look straight down upon the edge of the Day 
and Night Circle you see the lines of sunrise and of sunset also lying 
exactly north and south at right angles to the equator. We shall see 
later that this is not always so. 

It is important that the pupils should here be taught a little scientific 
use of the imagination. Some of them, seeing the sun represented so 
small and so close to the earth, may not, without aid, clearly understand 
how it can illuminate at once the whole of a hemisphere of the earth, so 
as to be seen simultaneously by inhabitants dwelling all around the edge 
of the Day and Night Circle as well as by those who are directly under 
the central ray. They should be told that the sun is immensely larger 
than the earth, but also very far away, so far in fact that lines of sight 
directed to the sun from any and all points on the side of the earth that 
happens to be turned toward him, are all parallel. One way in which 


4 





COSTELLO SOLAR DEMONSTRATING GLOBE 


the teacher can make this evident is by balancing a ruler over the top of 
the globe and showing that it is parallel with the central ray of the sun. 
Then, moving the ruler around the circumference of the Day and Night 
Circle, he can show that the parallelism exists at every point. 

Angular Rate of the Earth’s Rotation 

Having observed how the eastward rotation of the earth on its axis 
causes the sun to travel westward around the globe, carrying sunrise, 
noon, and sunset with it, as if daylight were a cap covering half the globe 
and continually slipping around it toward the west, let us now fix our 
attention on the equator. Notice that it is divided (as all circles always 
are for mathematical purposes) into 360 equal parts, called degrees. 
Now, there are 24 hours in the period of one rotation of the earth, called 
a day, and 360 divided by 24 gives 15; from which we see that the 
earth must turn in its daily rotation through 15 degrees in one hour. 
This is a very important fact to be committed to memory. It is with 
reference to this fact that the meridians of longitude are drawn on the 
globe at intervals of 1 5 degrees. If we set the sun over any one of these 
meridians and then rotate the globe until the next meridian westward 
comes under the sun we shall have turned the globe just as far, angularly, 
as the earth turns in one hour. And, since there are 60 minutes in an 
hour, and it takes the earth an hour to turn 1 5 degrees, if we rotate the 
globe only one degree we shall have turned it as far as the real earth 
turns in 4 minutes. This is another most important fact to be always 
carried in the memory, viz. that in every four minutes of time the earth 
turns one degree eastward around its axis, while during the same time 
the sun appears to move one degree westward through the sky. We shall 
have frequent occasion to use this while working with the semi-tellurian. 


b 



COSTELLO SOLAR DEMONSTRATING GLOBE 


THE SUN’S YEARLY MOTION—THE SEASONS 



We next consider the ecliptic, or the sun’s yearly path. This, as we 
have already seen, is drawn upon the globe, crossing the equator at two 
opposite points. For convenience it is represented as if it lay upon 
the earth instead of running around the background of the sky. Now, 
just as the division of the equator into degrees enables us to measure the 

angular distance that the earth 
rotates during any given time, as 
one hour, or four minutes, so the 
divisions that we see on the 
ecliptic enable us to measure the 
distance that the sun advances 
during a given time in its yearly 
course around the earth. But on 
the ecliptic each division marks 
not one degree but one day. So 
we see that the earth makes one 
rotation (through 360 degrees) 
while the sun is going forward 
about one degree on the ecliptic. 
The correspondence would be 
exact if the year were just 360 
days long. 

Observe that as the ecliptic 
is drawn on the globe, the 1 st 
of January falls at a point off 
the west coast of South America, 
but the sun’s yearly journey is 
assumed to begin on March 2 1, 
which, in order to bring the 
astronomical and geographical 
prime meridians into accord, is 
represented on the globe as ly- 
, _ , .. . . ing on the meridian of Green- 

Position of Earth March 21st. . , , . t • .1 

Vernal Equinox. wich at the point where the 

equator and the ecliptic meet 
and cross, and where we placed the sun when we were observing the 
sun’s daily motion, and the succession of day and night. 

This point on the ecliptic which the sun reaches every year about 
March 2 1 is called the Vernal Equinox, and the meridian running north 
and south through it is the equinoctial colure, or Prime meridian of the 
heavens. The meridian of the earth which corresponds to it, and passes 
through Greenwich, is called the Prime meridian of the earth. Longi¬ 
tude and time are reckoned from that meridian. 


Now, what we want first to show is how the sun advances eastward 
in the ecliptic, making a complete round in a year, and how, as it ad- 


6 








COSTELLO SOLAR DEMONSTRATING GLOBE 


vances, its position with reference to the equator continually changes. 
We begin by fixing the sun, as we did before, with its central ray over 
the point marked March 2 1 on the ecliptic and 0 degrees on the equator. 
Set the globe before you in such a way that the north pole of the axis 
inclines toward the right. Then the ecliptic will lie in a horizontal 
position. 

The sun is now at the point in the ecliptic which it occupies at the 
beginning of the astronomical spring. It is vertical over the equator, 
and as we shall see more fully 
length all over the earth. This 
is the origin of the word equinox. 

Without rotating the earth on its 
axis, advance the sun along the 
ecliptic toward the east by push¬ 
ing it together with the Day and 
Night Circle around toward the 
right, for you will observe that 
the dates marked on the ecliptic 
run that way. 

As soon as the sun is moved 
it leaves the equator and begins 
to approach gradually toward 
the north pole in consequence 
of the inclination of the ecliptic 
to the equator. By April 1 it is 
several degrees north of the 
equator. As we continue to 
push it eastward it glides yet 
farther from the equator and 
nearer to the north pole, until, 
when it has arrived over the 
date June 22, it is 2?>/i degrees 
north of the equator, and only 
66/2 degrees south of the pole. 

This is as far north as it can go, 
since its motions are confined to 
the ecliptic, and this point is 
called the Summer solstice, be¬ 
cause the ancients noticed that, 
at this time of the year the sun seems for a considerable period to return 
to about the same elevation in the sky at each successive noon. Solstice 
comes from the Latin words meaning “sun standing.” The Globe shows 
that for some distance on either side of June 22 the sun’s distance from 
the equator varies but slightly, because the ecliptic there runs nearly 
parallel with the equator. 

Now, if we continue to push the sun-ball around eastward, after 
leaving June 22 we see it decline again toward the equator, and on Sept. 
23 it once more crosses the equator, this time trending southward. Thus 
it returns to the southern hemisphere from which it emerged six months 


later, day and night are now of equal 



Position of Earth June 22nd. 
Summer Solstice. 


7 





COSTELLO SOLAR DEMONSTRATING GLOBE 


before at the Vernal equinox. The point where the sun crosses the equa¬ 
tor on Sept. 23 is called the Autumnal equinox, because then again day 
and night are of equal length all over the earth. 

But we must follow the sun still farther for as yet we have seen it 
perform only half of its yearly course. We keep on, then, pushing it 
around the ecliptic, being careful not to rotate the globe, and it moves 
farther and farther south of the equator, and nearer and nearer to the 
south pole, until, on Dec. 22, it reaches its farthest southern position, 
23J/2 degrees below the equator, and there arrives at the Winter solstice, 
exactly resembling the Summer solstice except that it occurs when the sun 
is as far south of the equator as it can go, while the Summer solstice 
occurs when it is as far north as it can go. But for people who live south 
of the equator our Winter solstice is their Summer solstice and vice versa. 

To complete the sun s yearly journey around the ecliptic we push 
it on eastward from Dec. 22, watching it now approach again toward the 
equator until on March 2 I, one year after its start, it once more reaches 
the equator at the Vernal equinox, and mounts again into the northern 
hemisphere, bringing back spring and summer in its train. 

Now, this alternate northward and southward gliding of the sun with 
respect to the equator is due entirely to the inclined position of the earth s 
axis. A very striking proof of this is obtained if we look at the situation 
of the earth’s poles when the sun is at March 2 1. Then both poles are 
seen to be under the Day and Night Circle, but inclined 23J/2 degrees 
from the central points at the top and bottom of the Circle. Those 
points represent the poles of the ecliptic, as if that, too, had an axis run¬ 
ning through its center at right angles to its plane. Now push the sun 
around to June 22; then the north pole projects out of the Day and Night 
Circle 23 J/2 degrees toward the sun, while the south pole projects an 
equal distance away from the sun. Put the sun at Dec. 22, and it is the 
south pole that projects toward the sun and the north pole away from it. 
Thus it is evident that the ecliptic circle is like an equator for the poles of 
the ecliptic, and that since in its yearly motion the sun always remains 
in the plane of the ecliptic circle, it is compelled to be six months above 
and six months below the plane of the earth’s equator. 

Here then, plain before the eyes, is the cause of all those wonderful 
changes of temperature, of sunlight, of green fields succeeding blankets 
of snow, and of blizzards chasing close upon the heels of soft Indian sum¬ 
mer days, which we group under the sober name of seasons, or seasonal 
change. If the earth’s axis had stood upright to the plane of the ecliptic 
summer and winter would have known and kept their places, instead of 
driving one another to and fro across the equator, while equator and 
ecliptic would have been merged in a single plane. 


8 



COSTELLO SOLAR DEMONSTRATING GLOBE 


WHY SUMMER IS HOT AND WINTER COLD 



At this point attention may be called to the principal cause of the 
contrast of temperature between summer and winter. It is the change 
of inclination of the sun’s rays to the surface of the earth. Start with the 
sun at the Summer solstice, (June 22), and rotate the earth until America 
is on the meridian with the sun. We see that at this time the United 
States lie, so to speak, full face toward the sun, and the solar rays descend 
almost perpendicularly upon the 
southern point of Florida, and 
the mouth of the Rio Grande. 

When the sun’s rays fall at so 
small an inclination more of 
them are received on a given 
amount of surface and the heat 
is proportionally intense. 

But now advance the sun to 
Sept. 23 (the Autumnal equi¬ 
nox) and rotate the earth until 
America is on the meridian, and 
you find that, as seen from the 
direction of the sun, the surface 
of the United States is very much 
more inclined to the solar rays 
falling upon it than was the case 
on June 22, and consequently 
those rays are less effective than 
they were three months before, 
so that the cooler days of Au¬ 
tumn now approach. 

Next push the sun on to Dec. 

22 (the Winter solstice), and 
observe, when America is on the 
meridian, that the northern part 
of the United States seems to lie 
away over the shoulder of the 
earth, sloping away from the 
sun, so that the rays now fall at 
a low angle, even on the southern states, and consequently are much less 
effective for heating and lighting than they were even in September, and 
still less than they were in June. Now is the season of the snows. In 
the meantime South America has moved up, as it were, right under the 
sun, and s Duthern Africa, and Australia, as can be seen by rotating the 
globe, are now having their hottest weather. 


Position of Earth Sept. 23rd. 
Autumnal Equinox. 




COSTELLO SOLAR DEMONSTRATING GLOBE 


THE SUN’S TWO MOTIONS COMBINED 



Heretofore we have been studying separately the two motions of 
the sun—the daily and the yearly,—now let us consider the effects of 
their combination, for of course they both go on together. If the earth 
simply travelled around the sun, with its axis inclined as it now is, but 
without rotating, there would be but one day and one night in a year, 
and every place on the earth would have six months of daylight fol¬ 
lowed by six months of dark¬ 
ness. Then if the sun could 
draw a continuous photographic 
line on the earth as the earth 
went around him that line would 
coincide with the ecliptic circle 
drawn around the Globe. But 
the daily rotation of the earth 
changes this so that the single 
photographic line would be 
spread into a band of close- 
packed spirals covering all the 
space between the Tropics, as 
the sun winds its way now north¬ 
ward and now southward. 

But for our purposes we 
may imagine the sun as remain¬ 
ing during each successive day 
at an unvarying distance from 
the equator, i. e. with its decli¬ 
nation fixed during 24 hours. 

We start with the sun on the 
Prime meridian, at March 21, 
or the Vernal equinox. Now, 
keeping the sun fixed in position 
and, before rotating the globe, 
observe again what we saw in a 
„ _ . former demonstration, viz. the 

Position of Earth Dec. 22nd. . . , . , f 1 l* Li. 

Winter Solstice. hemispherical cap ot daylight ex¬ 

tending from the sun’s central 
ray 90 degrees in every direction, north, south, east, and west, until its 
border is formed by the Day and Night Circle. Notice that the Day 
and Night Circle passes over both poles, and cuts the equator at right 
angles on both sides. Since both poles are on this line between day and 
night, both are reached, at the same time, by the sun’s rays—just reached 
and no more, for as seen from either pole the sun would now appear to 
lie on the horizon. 

(Either at this point or later, the teacher may explain the effects 
of twilight and atmospheric refraction, to which we shall devote a few 
words further on). 






COSTELLO SOLAR DEMONSTRATING GLOBE 


Now, leaving the sun fixed in position, rotate the globe on its axis 
from west to east. The sun follows the equator westward, crossing the 
meridians one after another as they move eastward under him. Observe 
that as each meridian passes under the Day and Night Circle it is parallel 
with that Circle. While the globe is rotating place yourself in imagina- 



Position of Earth March 21st. 
Vernal Equinox. 


tion standing on either the north or the south pole. You see that you 
could have one foot on the daylight side and the other on the night side 
of the line between day and night (if that were a perfectly sharp line), 
so that as the earth turned, you would see the sun apparently running 
around you on the horizon, with half of its disk above and the other 
half below. 


11 



COSTELLO SOLAR DEMONSTRATING GLOBE 


THE TIME OF EQUAL DAYS AND NIGHTS 

But here is a thing of more practical importance to everybody. 
Notice that as the earth rotates, with the sun in the position that it oc¬ 
cupies on March 2 1, day and night are of equal length everywhere on 
the globe. This is evident because, as you can see by looking straight 
down upon the edge of the Day and Night Circle, the line between day 
and night cuts every parallel of latitude from the equator to both poles 
exactly in half. This being so, and every place on the globe being car¬ 
ried around on its own parallel of latitude as the earth rotates, every 
such place must be half of the 24 hours in the daylight and the other 
half in the night. 

But it is instructive to demonstrate this by actually rotating the 
globe. Take, to begin with a place on the equator. Let it be Quito in 
South America. Without moving the sun, turn the globe until Quito is 
exactly under the sunrise (left-hand) edge of the Day and Night Circle. 
Then place the Quadrant on the meridian of Greenwich, with its arrow 
pointing to 0 degrees on the equator, and tighten the screw at the north 
pole to hold the Quadrant firmly in position. Next rotate the globe from 
west to east until Quito comes under the sunset (right-hand), edge of the 
Day and Night Circle. Now count along the equator the number of de¬ 
grees that the point of the Quadrant has passed over, moving westward 
from the Greenwich meridian. You will find that the distance moved is 
l 80 degrees, or just one-half way round the globe, i. e. one half of a 
complete rotation of the earth. But since a whole rotation takes 24 hours 
it is evident that half a rotation must take 1 2 hours, from which we see 
that at the Vernal equinox, the length of the day at Quito, on the equa¬ 
tor, is 1 2 hours, leaving 1 2 hours for the night. If we try the same ex¬ 
periment with any other place lying on the equator we get the same 
result. 

This demonstrates that all around the equator on March 2 1, day 
and night are of equal length; but are they of equal length at all other 
points on the earth? Yes, and to prove it let us take Chicago, which is 
almost 42 degrees north of the equator. Place Chicago under the sunrise 
edge of the Day and Night Circle, then set the Quadrant pointing to 0 
degrees on the equator, rotate the globe eastward until Chicago comes 
under the sunset edge, and count the number of degrees that the Quad¬ 
rant has moved westward. It is again 180 degrees, showing that the 
earth has rotated just half way round in carrying Chicago from the sun¬ 
rise to the sunset, so that the day must be 1 2 hours long at Chicago, just 
as it is at Quito. If you repeat the demonstration for any other place, 
anywhere on the globe, you get precisely the same result. 

Notice one other thing and remember it for comparison afterward; 
since the meridians as they pass under the Day and Night Circle are all 
parallel with that Circle, it is evident that at the time of the equinox all 
places lying on the same meridian of longitude, i. e. the same north-and- 
south line, must have sunrise and sunset, and also noon, at the same 
absolute time. 


12 



COSTELLO SOLAR DEMONSTRATING GLOBE 


To finish with the study of what happens when the sun is vertical 
over the equator, fix the sun over the date Sept. 23 (the Autumnal equi¬ 
nox), and repeat the demonstrations above described, observing that the 
same results are obtained as to the equality of day and night everywhere, 
and that, just as at the Vernal equinox, daylight extends from pole to 
pole. But remember that this condition exists only at the two equinoxes, 
for at all other times of the year, except exactly on the equator, day and 
night are unequal. 

Unequal Days and Nights 

We shall now study the phenomena and causes of days and nights 
unequal in length. It will be recalled that, when we were considering 
the yearly march of the sun around the ecliptic, we found that after 
March 2 1 it began to depart northward from the equator, arriving on 
June 22 at its farthest northern declination, 23J/2 degrees. Let us now 
place the sun at June 22 on the ecliptic. (You will find the point marked 
on the globe near Calcutta, India). Now you see the north pole leaning 
toward the sun, the consequence of which as affecting the temperature 
we have already pointed out. 

Rotate the globe on its axis and not only the north pole, but a 
great circular area around it, covering more than eight million square 
miles, the south border of which is indicated by a dotted circle 23J/2 
degrees from the pole, marked “Arctic Circle,’’ remains wholly and con¬ 
stantly in the sunlight, while the south pole is surrounded by a similar 
circle, the “Antarctic Circle,’’ within which, as the globe rotates, the sun 
does not rise at all. 


13 



COSTELLO SOLAR DEMONSTRATING GLOBE 


WONDERFUL PHENOMENA AT THE POLES 

The north pole is now in the middle of a period of six months dur¬ 
ing which the sun never sets upon it, while the south pole is in the middle 
of a similar period during which the sun never rises upon it. Imagine 
yourself again standing on the north pole. Any direction that you choose 
to look over the earth s surface is south. The whole earth lies south of 
you. The circle of the horizon as it runs around you is everywhere south 
of your position. If there is any north at all for you it is directly over 
your head, in the zenith. West and east are directions indicated only by 
the way you are turning on a vertical axis with the earth’s rotation. 

The sun appears 23 J/£ degrees above the horizon, slowly circling 
around you from east to west but keeping at the same elevation. That 
is one way in which an explorer can tell when he is on the pole. If you 
set up a stake in front of you, and in line with the sun and keep facing 
the stake, then in 24 hours the sun will have gone all around the sky 
behind you and come back into line with the stake. (Of course it is you 
and the stake that have really been in rotation). 

Now imagine yourself starting from the pole and walking straight 
south along any meridian. As you go on, the circle that the sun de¬ 
scribes in 24 hours will be tipped more and more to the plane of the 
horizon. You will again have a direction north—the direction of the 
pole—and when you have gone say 1 0 degrees from the pole, or nearly 
700 miles, the sun’s circle of revolution in the sky will be elevated about 
33J/2 degrees above the horizon directly in the south, but only about 
13!/ 2 degrees above it directly in the north. Keep on until you reach 
the Arctic Circle. Then, when the sun is south, it will be 47 degrees 
above the horizon, and when it is north it will lie right on the horizon. 

This is the celebrated phenomenon of the “Midnight Sun,’’ which is 
visible at the time of the Summer solstice, in Norway and Alaska, and, in 
fact, anywhere around the Arctic Circle. The name comes from the fact 
that it is midnight at all points south of the Arctic Circle at the moment 
when, on or near that Circle, the sun just touches the northern horizon. 

But if at the Summer Solstice you started from the south pole, you 
would walk in darkness until you reached the Antarctic Circle, and there, 
when the sun was exactly north it would just come up for a moment to 
the horizon, like a fish timidly touching the water surface from below, 
and then sink out of sight. 

(In these illustrations the declination of the sun is supposed to re¬ 
main unchanged while the observer is changing his position). 


14 




COSTELLO SOLAR DEMONSTRATING GLOBE 


DAY AND NIGHT INSIDE THE POLAR CIRCLES 


The Costello Globe affords an admirably graphic means of illus¬ 
trating the way in which the Arctic and Antarctic nights and days 
lengthen between equinox and solstice, and shorten between solstice and 
equinox, while the area around the pole within which the sunlight or 
darkness is continuous for a certain period, alternately expands and con¬ 
tracts. For this purpose, start again with the sun placed over March 21, 
and the north pole inclining toward the right so that the ecliptic will lie 
horizontal. 


Then stand in such a position that you can look down upon the 
north pole, and, without rotating the earth, push the sun around the 
ecliptic toward the east. You will see the Day and Night Circle move 
away from the pole and approach the Arctic Circle, while the pole passes 
out into full sunlight, and around it expands an ever widening circular 
area lying, like the pole, entirely inside the sunrise line. This will con- 
1 sun is over June 22, the Summer solstice, when the Day 
and Night Circle will have receded away 23Y 2 degrees from the pole and 
will lie tangent to the Arctic Circle. At that moment it is evidently per- 
petual day everywhere within the Arctic Circle. 


But continue to push the sun around the ecliptic eastward, and 
quickly you will see that the Day and Night Circle is returning poleward 
so that it is no longer perpetual day on the Arctic Circle, and the circular 
area covered by perpetual day will grow smaller until the sun reaches 
Sept. 23, when again the Day and Night Circle lies over both poles, and 
day and night are equal all over the earth. 


Keeping on after Sept. 23 the Day and Night Circle will be seen 
retreating again from the north pole but this time in such a direction as to 
cause the pole to move into the night side and to go deeper and deeper, 
until Dec. 22 when the night area has spread as far out as the Arctic 
Circle. (I he teacher may add many details to this illuminating demon- 
stration which will increase its interest to the pupils). 


15 




COSTELLO SOLAR DEMONSTRATING GLOBE 


DAY AND NIGHT BETWEEN THE EQUATOR AND THE POLAR 

CIRCLES 



Now, having seen what the phenomena of day and night are around 
the poles at the Summer solstice, let us examine the conditions at that 
same time on the other parts of the earth. Place the sun back over June 
22. Rotate the earth from west to east, and the sun, keeping 23J /2 de¬ 
grees north of the equator, runs around the earth, following a dotted line 
marked “Tropic of Cancer.” Starting from Calcutta in India, it passes 

over the center of Arabia, the 
desert of Sahara, the Central 
Atlantic, the Gulf of Mexico, the 
Pacific ocean, southern China, 
and so back to Calcutta. All 
along that line, on June 22, the 
sun is vertical, or in the zenith. 
(It is not quite vertical through¬ 
out the circuit, because its decli¬ 
nation is slowly changing, but 
we neglect this). To all the in¬ 
habitants of the earth south of 
the Tropic of Cancer the sun, at 
noon, appears north of the 
zenith, and farther north in pro¬ 
portion as they are farther 
south; while to all the inhabit¬ 
ants north of the Tropic of Can¬ 
cer, the noon sun is south of the 
zenith, and farther south as they 
are farther north. Observe that 
just as far as the Tropic of Can¬ 
cer is north of the equator so far 
does the daylight extend beyond 
the north pole, on the side away 
from the sun. 

To see the effects of this on 

Position of Earth June 22 with Chicago under the length of day and night, let 
the Sunrise Line and the quadrant set on the us Lack to Chicago, which is 

meridian of Greenwich. , i o l . i f ,i 

about I o degrees north ot the 
Tropic of Cancer. We put Chicago under the sunrise line, set the Quad¬ 
rant on the meridian of Greenwich, pointing to 0 on the equator, and 
rotate the globe eastward until Chicago is under the sunset line. Then 
we count the number of degrees that the Quadrant has swept westward 
on the equator, from the meridian of Greenwich, and find it to be about 
226. Multiply this number of degrees by 4 to reduce it to minutes of 
time, and you get 904 minutes, which divided by 60 minutes to the hour, 
gives 1 5 hours and 4 minutes for the length of the day, or the length of 


16 








COSTELLO SOLAR DEMONSTRATING GLOBE 



time that the sun remains above the horizon at Chicago on June 22. 
Subtracted from 24 hours, this leaves 8 hours 56 minutes for the length 
of the night. (The above result is a few minutes shorter than the length 
of the day shown by almanacs because we take no account of atmos¬ 
pheric refraction, whose effect is to hasten the apparent time of sunrise 
and delay the apparent time of sunset). 

Now, compare the result that we have just obtained with that which 
we got when the sun was at the Vernal equinox. Then day and night at 
Chicago were of equal length, each being 1 2 hours long, but now, three 
months later, day is about six hours longer than night. Why is this? 
We can easily show why by putting Chicago again under the sunrise line, 
and rotating the globe eastward, 
while keeping the eye fixed on 
Chicago as it is carried around. 

We see that, owing to the incli¬ 
nation of the north pole toward 
the sun, the arc passed over by 
Chicago in traversing the day¬ 
light side of the globe is much 
longer than the arc that it passes 
over in going around through 
the night side. This difference 
is also evident if we simply fix 
attention upon the parallel of 
latitude of 40 degrees which 
runs around a little below Chi¬ 
cago, and note how much longer 
that part of it is which lies on 
the sunlit half of the globe. 

If you take any other place, 
anywhere on the same parallel 
of latitude with Chicago, no mat¬ 
ter how far east or how far west 
it may be, you will find the same 
length of day and night as at 
Chicago. But if you take a place 
lying either farther north or 
farther south than Chicago you 
find a different length of day. 

It will be longer if the place is 
farther north, and shorter if the 
place is farther south. This, like the equality of day and night at the 
equinox, is evident by inspection, for if now again we look down upon 
the edge of the Day and Night Circle we see that it cuts all the parallels 
of latitude into two unequal parts, the longer part, or arc, lying on the 
daylight side and the farther north we go the more the daylight arc ex¬ 
ceeds the night arc in length. If we go as far as the Arctic Circle we find 
that the Day and Night Circle does not cut that at all, but leaves it en¬ 
tirely on the daylight side. 


Position of Earth June 22nd with Chicago under 
the Sunset Line with quadrant on the 13 4th 
degree East. 


17 




COSTELLO SOLAR DEMONSTRATING GLOBE 


However, as in the other case, it is instructive and interesting to 
demonstrate this inequality by rotating the globe under the solstitial sun. 
For this purpose take Juneau in Alaska, and rotate it, as we did Chicago, 
from sunrise to sunset (always setting the Quadrant anew on the Green¬ 
wich meridian for every new place that we try), and we find that the 
Quadrant turns through 262 /i degrees, which reduced to time gives 17 
hours 30 minutes for the length of day at Juneau when it is 13 hours 4 
minutes at Chicago. Going still farther north, to the Arctic Circle, we 
find that there, day becomes 24 hours long, and night, for that one date, 
vanishes. 

Then, going in the other direction, try the city of Mexico, more than 
20 degrees south of Chicago, and you find that its day is only 1 3 hours 
1 2 minutes, when Chicago’s is 1 5 hours 4 minutes. And if you keep on 
going south until you reach the equator, you find that the day shortens 
and shortens until, just on the equator, it becomes again exactly equal in 
length to the night—12 hours each. Thus at Quito, or at any other 
point on the equator, day and night are equal at all times of the year, 
while for other parts of the earth they are equal only at two opposite 
times in the year, viz. the Vernal and the Autumnal equinox. 

In general, if we fix attention on any one particular place (not sit¬ 
uated on the equator) we find that its days lengthen and its nights shorten 
as long as the sun is rising higher above the equator, but when the sun is 
sinking the days shorten and the nights lengthen. On the other hand, 
if we shift the place and fix attention on some particular date (excepting 
the two equinoxes) the length of the day increases as the latitude of the 
place is greater and decreases as the latitude is less. 

In our demonstrations we have dealt only with the northern hemis¬ 
phere, but precisely similar results will be obtained for places south of 
the equator, except that when the days are longer than the nights in one 
hemisphere they are proportionally shorter than the nights in the oppo¬ 
site hemisphere. 

In making these demonstrations it is not necessary to choose only 
the dates of the equinoxes or the solstices; they show the extreme condi¬ 
tions, but any other time of the year may be taken. For a single illus¬ 
trative instance, take Aug. 1 5, and let the place be Chicago. Fix the sun 
over the date Aug. 1 3 on the ecliptic, and then proceed as in the other 
cases. We thus find that the length of the day at Chicago in mid-August 
has become only 13 hours 44 minutes. You may make a similar demon¬ 
stration for any place, on any date. (Never forget to set the Quadrant 
on the Greenwich meridian after putting the chosen place on the sun¬ 
rise line). 


18 



COSTELLO SOLAR DEMONSTRATING GLOBE 


THE TIMES OF SUNRISE AND SUNSET—AT THE EQUINOXES 

We now come to the question of telling the hours of sunrise and 
sunset, which the Costello Globe enables us to solve with the greatest 
ease. 



We begin once more at one of the equinoxes—say the Vernal. We 
set the sun over the date March 2 1, and we take a place on the equator, 
say Quito, and bring it under the sunrise line; then we set the Quadrant 
pointing to 0 degrees on the 
equator (meridian of Green¬ 
wich), after which we rotate the 
globe eastward until Quito 
comes vertically under the cen¬ 
tral ray of the sun-ball. This 
means that Quito has passed 
from sunrise to noon, and now 
has the sun in its zenith. Count¬ 
ing the number of degrees that 
the Quadrant has swept west¬ 
ward on the equator we find 
that it is just 90, which corres¬ 
ponds to six hours of time. So 
we see that at a place on the 
equator, at the time of the equi¬ 
nox, the sun rises six hours be¬ 
fore noon, i. e. at six o’clock A. 

M. (It should be remarked that 
we are referring throughout this 
manual not to “standard time,’’ 
or “daylight saving” time, but 
to local solar time). If we con¬ 
tinue the earth’s rotation until 
Quito reaches the sunset line, we 
shall find that the sun sets there 
six hours after noon, or at six 
o’clock P. M. 

So much for the hours of sun¬ 
rise and sunset for places on the 
equator. (Stanleyville in the middle of Africa is another place on the 
equator that you might try). Now let us go north to Chicago. We 
place Chicago under the sunrise, reset the Quadrant, and rotate the globe 
until Chicago is on the noon line, which means the meridian, or north- 
and-south line, running under the central ray of the sun-ball. It was easy 
to bring Quito to the noon line because the place came right under the 
sun, and if the meridian running through Chicago were marked on the 
globe it would be equally easy to bring Chicago to the noon line simply 
by carrying its meridian under the center of the sun. As it happens, 


Position of Earth March 21st with Chicago under 
the Sun’s noon ray and the quadrant on the' 90th 
meridian West. 


19 



COSTELLO SOLAR DEMONSTRATING GLOBE 


however, Chicago is more than two degrees east of the 90th meridian 
marked on the globe, and since the distance between the meridians in¬ 
creases as the latitude decreases, it is necessary to use a little care and 
judgment in placing Chicago on the same meridian, with the sun. Hav¬ 
ing placed it so, we again count the degrees that the Quadrant has moved 
on the equator, and find the number to be again 90, just as it was for 
Quito. This proves that, at the equinoxes sunrise occurs everywhere on 
the earth at six o'clock A. M. and sunset at six o’clock P. IVL T corres¬ 
ponding with the equality in the length of day and night at the equinoxes, 
which we demonstrated before. 


At the Solstices 



Next let us see what happens 
at the solstices—say the Sum¬ 
mer solstice, which occurs June 
22, when the sun is vertical 
along the circle of the Tropic of 
Cancer, 23J/2 degrees north of 
the equator. If, with the sun 
placed over the date June 22, 
we repeat with Chicago what we 
did at the equinox we find that, 
in carrying Chicago from the 
sunrise to the noon line the earth 
turns about 1 1 3 degrees on its 
axis, corresponding to 432 min¬ 
utes of time, or 7 hours 32 min¬ 
utes. Remark that this is the 
length of time that elapses be¬ 
tween sunrise and noon, and to 
find out what the time of sunrise 
shown on the dial of a clock 
keeping local time is, we must 
subtract the 7 hours 32 minutes 
from 12, the number of hours 
between midnight and noon. 
The subtraction leaves 4 hours 
28 minutes, which is the sunrise 
time. (This makes no allow¬ 
ance for atmospheric refraction, 
or other corrections). 

To find the time of sunset we have only to reverse the subtraction 
that we made before by taking the sunrise time from 12 hours; or we 
can use the figures found at first for the number of hours between sun¬ 
rise and noon, because these represent also the number of hours between 
noon and sunset. (If we were seeking very exact results we would have 
to allow for the hourly movement of the sun in the ecliptic). If it is 
desired to find the time of sunset directly, it can be done by starting with 
Chicago on the noon line, with the Quadrant fixed at 0 degrees, rotating 


Position of Earth June 22nd with Chicago under 
the Sun’s noon ray and the quadrant on the 
113th degree West. 


20 




COSTELLO SOLAR DEMONSTRATING GLOBE 


the globe until Chicago is under the sunset line, and then, as before, 
counting the degrees passed over by the Quadrant. Reducing these to 
time gives the time of sunset without any subtraction. 

Note that for any other place lying on the same parallel of latitude 
the times of sunrise and sunset are the same as at Chicago. But north of 
Chicago the sun rises earlier and sets later than at Chicago, while south 
of Chicago the sunrise occurs later and the sunset earlier. 

We have before noticed that at the equinoxes the sunrise and sunset 
line lie parallel with the meridians of the earth, and at right angles to the 
equator. This is not the case at any other time of the year, (although it 
is always true of the noon line), and the variation is greatest at the 
solstices. It is this that causes the difference in sunrise and sunset times 
between places having different latitudes. A very interesting effect is 
seen by placing for instance Chicago on the sunrise line at the time of the 
Summer solstice, and observing the sloping direction which that line takes 
in crossing the United States. Instead of running north and south it 
runs from the western end of Lake Superior through Chicago, through 
central Indiana, passing near Louisville, Ky., and so on, south-eastward, 
until it emerges into the ocean between Savannah and Charleston and 
thence goes on across the Bahama islands. All along that line early 
risers see the sun coming up at practically the same moment that it is seen 
at Chicago. But they do not all see it crossing the meridian at the same 
time, as you can prove by putting Chicago at noon, and noting the direc¬ 
tion of the noon line. 

And now see how very different the situation becomes at sunset. 
Put Chicago on the sunset line, and observe that its course across the 
United States is from Sault Ste Marie through Chicago, St. Louis, the 
south-western corner of Arkansas, eastern Texas, crossing into Mexico 
above the mouth of the Rio Grande and passing not far west of Mexico 
City, and so out across the Pacific ocean. All along that line people see 
the sun set at practically the same moment as at Chicago. But what a 
different company it is from that which lined up to see the sun rise! 

At the equinoxes the line runs exactly north and south, (as it al¬ 
ways does, everywhere, at noon), and New Orleans and Chicago see the 
sun both rise and set at nearly the same time, but when we go on to the 
Winter solstice (Dec. 22) we get the lines of sunrise and sunset crossing 
again, only this time their directions are exactly reversed, the sunrise line 
running south-west from Chicago and the sunset line south-east. 


21 




COSTELLO SOLAR DEMONSTRATING GLOBE 


REFRACTION 

The gaseous atmosphere surrounding the earth and consisting main¬ 
ly of a mixture of oxygen and hydrogen, possesses like all transparent 
media the power to refract, or bend out of their original course, rays of 
light passing into and through it. The refraction increases with the den¬ 
sity of the air, and consequently is greater with rays passing through the 
lower and denser layers of the atmosphere than with those which pass 
only through the rarer layers overhead. Directly in the zenith there is 
no refraction, but as the horizon is approached the refraction increases 
nearly as the tangent of the angular distance from the zenith. Just at 
the horizon the amount of the refraction becomes, on the average, a little 
more than half a degree, but it varies more or less with the changing 
density and temperature of the air. Now, the refraction acts in a vertical 
direction, so that the rays of light coming from a distant body close to 
the horizon are bent downward between the object and the observer s 
eye, the effect being that the object appears to be lifted higher above the 
horizon than it really is. Since the angular diameter of the sun is about 
half a degree (the same as the amount of the refraction) it is evident that 
the refraction is capable of lifting the sun into view after it has really 
just sunk beneath the horizon. So, under ordinary circumstances, in a 
fairly level country, when you see the sun apparently resting with its 
lower rim on the horizon it is really wholly below with its upper rim only 
reaching the level of the horizon. Now, the daily motion of the sun, as 
we have before seen, carries it westward about one degree in four min¬ 
utes; hence two minutes are required for the sun to move its own 
diameter, so that when the sun is setting the refraction adds two minutes 
to the length of the afternoon. Conversely the refraction causes the sun 
to appear above the eastern horizon two minutes before its real rising; 
thus on the whole four minutes are added to the length of the daylight 
period, at the equator, where the sun rises and sets vertically, but the 
farther you go from the equator the more slopingly to the horizon does 
the path of the sun lie, and the longer the sun takes to rise and set, so 
that the refraction lengthens the day least at the equator and most in 
high latitudes. The lengthening effect also varies at a given place with 
the position of the sun in the ecliptic. In middle latitudes it varies from 
four to eight minutes. Another curious optical effect of refraction is to 
cause the disk of the sun (and also of the moon) to appear distorted 
when near the rising or setting point, the lower edge of the disk being 
lifted more than the upper edge so that it seems to be flattened in a ver¬ 
tical direction, or stretched out horizontally. 


22 



COSTELLO SOLAR DEMONSTRATING GLOBE 


TWILIGHT 

Another atmospheric phenomenon which affects the length of time 
during which illumination from the sun reaches a given place on the 
earth is twilight, which is visible both after sunset and before sunrise. 
The morning twilight is usually called dawn. Twilight is due to the il¬ 
lumination of the higher layers of the atmosphere up to the level where 
the air becomes so rare that no perceptible reflection of light is perceived 
from it. This is about 40 miles 
above sea-level, under average 
circumstances, and the twilight 
does not wholly disappear until 
the sun has descended about 1 8 
degrees below the horizon. That 
requires about an hour and a 
quarter, but where the sun s path 
lies slopingly to the horizon, the 
duration of twilight is increased. 

In middle latitudes it is stretched 
out to about two hours in mid¬ 
summer. On the equator the 
duration is at a minimum because 
there the sun rises and sets ver¬ 
tically. Immediately after sun¬ 
set, or immediately before sun¬ 
rise, the twilight is almost as 
bright as moderate daylight, and 
for an hour or more in summer 
evenings daylight occupations 
may be continued in the grad¬ 
ually cooling and darkening air. 

The morning twilight is more 
stimulating if not more refresh¬ 
ing. It is a blessing that we owe 
entirely to the atmosphere. 

There can be no twilight on the moon. 

, remar kable effect of twilight is seen in the polar regions, where 

the illumination of the sky before sunrise and after sunset adds weeks of 
partial daylight to the long Arctic and Antarctic days. This is clearly 
demonstrated by the Costello Globe. First place the Globe before you 
w!th the sun at the Autumnal equinox, (Sept. 23) with the north pole 
inclined this time, to the left. The plane of the ecliptic will be horizon¬ 
tal. I he pole is now under the Day and Night Circle. But move the 
sun eastward on the ecliptic and immediately the line between day and 
night begins to swerve away from the pole, leaving it in darkness. It is 
the beginning of the long polar night (the effect of such a demonstration 
is much heigthened if the Globe is placed near a window, with the ni-ht 



23 





COSTELLO SOLAR DEMONSTRATING GLOBE 


side of the Day and Night Circle kept in shadow). Owing to refraction 
the sun will probably not set at the pole before about Sept. 25. Keep 
on moving the sun eastward, and the pole sinks deeper into the night. 
But remember that twilight lasts until the sun is 18 degrees from the 
horizon. Continue, then, to push the sun eastward until the Day and 
Night Circle has retreated 18 degrees from the pole. You can measure 
the distance by setting the Quadrant in line with the sun, and counting 
its graduations. Thus you will find that, when the sun is 18 degrees 
below the horizon of the pole, i. e. 18 degrees below the equator, it is 
near the date Nov. 1 4. This means that evening twilight at the pole has 
lasted from Sept. 25 to Nov. 14, a period of 50 days, instead of lasting 
only an hour or two as it does in the middle latitudes. 

Moreover if you trace the course of the sun back again through the 
succeeding months you find that after having sunk 23J/2 degrees below 
the polar horizon and the equator, on Dec. 22, it returns to only 18 de¬ 
grees below at the end of January leaving another period of about 50 
days before it rises on the pole at, or a little ahead of, the Vernal Equi¬ 
nox. This is the north pole s morning twilight or dawn. Putting the 
two together we get about 1 00 days of twilight at the pole, which makes 
daylight and twilight together last 280 days leaving only 80 days, or 
less than three months, for the yearly duration of nocturnal darkness. 
This shows that as far as the total duration of light in a year is concerned 
the poles are favored above all other places on the earth. 


24 



COSTELLO SOLAR DEMONSTRATING GLOBE 


PRECESSION OF THE EQUINOXES 

The inclination of the earth s axis from a perpendicular to the plane 
of the ecliptic is so important in its effects that the facts concerning it 
need to be presented a little more fully than they have appeared in the 
demonstrations thus far described. The future of the inhabited globe is 
deeply concerned in a fact which we have not hitherto mentioned, viz. 
that the direction in space of the inclined axis of the earth is slowly 
changing. The result of this change is that in a period of about 25,800 
years the north pole, (we need consider but one of the poles though 
both are similarly affected), makes a revolution around the north pole 
of the ecliptic in a circle of 23J/2 degrees radius. At the present time 
the north pole points very nearly toward the star known as Polaris, or 
the North Star; but 12,500 years hence it will point about 47 degrees 
away from that star, and within a few degrees of the very brilliant star 
Vega in the constellation Lyra. This revolution of the poles of the equa¬ 
tor around the axis of the ecliptic, is known as the Precession of the Equi¬ 
noxes, because an important consequence of it is that the crossing points 
of the equator and the ecliptic slowly shift around westward, and in 
12,500 years the Vernal equinox will be where the Autumnal equinox is 
now, But the yearly change is very slight, amounting to about 1 /72 
of a degree, or 50 seconds-of-arc. The cause of the Precession is the 
attraction of the sun and moon upon the protuberant equatorial part of 
the earth, which is slightly swelled at the equator and drawn in at the 
poles. The result is a gyroscopic motion of the rotating earth recalling 
the revolution of the peg of a top that is spinning with its axis inclined 
instead of upright. The angle of slope of the earth s axis remains almost 
constant while the direction in which the axis points swings around. 

Now, in order to understand the most important effect of the Pre¬ 
cession it is necessary to remember that the earth’s path, or orbit, around 
the sun is not an exact circle but a slightly eccentric ellipse, so that the 
sun being situated in one of the two foci of the ellipse, is farther from one 
end of the ellipse than from the other. The average distance of the earth 
from the sun being 93,000,000 miles, it is about three million miles 
nearer the sun when at the near end of its orbit, called Perihelion, than 
when at the far end and called Aphelion. But, owing to causes explained 
in works on astronomy, the orbit itself has a revolutionary movement 
which causes the Perihelion and Aphelion points to travel around east¬ 
ward in a period of about 108,000 years. Now, it so happens that at 
the present time the straight line, called the Line of Apsides, joining 
the Perihelion and Aphelion points, nearly coincides in direction with the 
line joining the Summer and the Winter solstice, and that the earth is at 
the Summer solstice when she is also near the Aphelion point, and at the 
Winter Solstice when she is near the Perihelion point. Thus, at the 
present time, we get our summer when the sun is most distant, and our 
winter when the sun is nearest. This causes the summer to be less hot 
and the winter to be less cold than would be the case if the winter oc¬ 


as 



COSTELLO SOLAR DEMONSTRATING GLOBE 


curred in Aphelion and the summer in Perihelion. But, owing to a com¬ 
bination of the effects of the Precession of the equinoxes, and the Revo¬ 
lution of the line of apsides, in about 10,500 years from now the condi¬ 
tions will be reversed, and then the earth will be in Aphelion in winter, 
and in Perihelion in summer. Moreover, since the earth travels slower 
when far from the sun than when near, the period from the Vernal to the 
Autumnal equinox is about a week longer than that from the Autumnal 
equinox back to the Vernal. This gives us at present a summer half of 
the year longer than the winter half. But ten thousand years from now 
the winter will be both colder and longer and the summer shorter, though 
hotter, than at the present time. It has been inferred that the conse¬ 
quence of such changes may be the occurrence of a very cold, or semi¬ 
glacial, period in the northern hemisphere. Of course the very condi¬ 
tions that we have been describing exist now in the southern hemisphere, 
but it is thought that the climatic excesses that they would otherwise pro¬ 
duce are mitigated or avoided by the presence in that hemisphere of 
vast oceanic expanses greatly exceeding those of the northern hemisphere 
which is a land hemisphere. The characteristic of an oceanic climate is 
relative mildness and equality. 


26 




COSTELLO SOLAR DEMONSTRATING GLOBE 


THE SUN 


The sun is a star, but we are so much nearer to it than to any of 
the other stars that while they appear as mere points of light, the sun 
appears as an immense blazing white ball about half a degree in diam¬ 
eter, and so bright that when it is above the horizon it makes daylight 
on the earth, and when it is out of sight below the horizon we are buried 
m the night in spite of the twinkling of those far-off other suns, the stars. 
Put the sun as far away as they are and it, too, would be but a twinkling 
point. 


Although the sun appears to be only a little more than half a de¬ 
gree in diameter, seen from the earth, 93,000,000 miles away, yet it is 
in reality about 866,000 miles in diameter while the diameter of the 
earth is only 8000. (The diameter of the star Betelgeuse in Orion has 
recently been found by measurement with the interferometer to be 300 
times the sun s, or about 260,000,000 miles!) 

The sun is globular in shape like the earth, but it would take more 
than twelve hundred thousand earths rolled into one to make a globe as 
large as the sun The surface of the sun is not solid and cool like that of 
the earth, but the whole body of the sun is a mass of intensely heated 
gaseous matter comprising, it is probable, all of the chemical substances, 
solid, liquid, and gaseous, of which the earth is made up, though their 
condition there is far different from their condition on and in the earth. 
At the surface of the sun they appear to be partially cooled and con¬ 
densed into incandescent clouds, but the enormous mass, or quantity of 
matter, in the sun causes so much pressure in its interior that, though the 
substances there are potentially in the gaseous state on account of the in¬ 
tense heat, yet they are prevented from expanding as they would do if 
released from the pressure These gases include such matter as iron 
which cannot become solid or even liquid there because of the heat. 

he heat of the sun apparently rises to a temperature of at least 10,000 
degrees at its surface It is radiated away in all directions together with 

Lro. nd h th and 80 rea j hes the earth and the other planets, which revolve 
around the sun at distances varying from 360,000,000 miles for the 

nearest up to 2,800,000,000 for the most distant known. There are 
eight principal planets of which the earth is the third in distance from the 
The largest planet Jupiter has about a thousandth part as much 

O^em fn mV Un ' ^ ^ P lanCtS ^ PUt to S ether the sun exceeds 

them in mass, or in power of gravitation, not less than 750 times. 


27 




COSTELLO SOLAR DEMONSTRATING GLOBE 


THE EARTH 

The earth is the fifth planet in order of size, beginning with the 
largest. Venus is of almost the same size, but Mars and Mercury are 
much smaller. Jupiter is as much larger than the earth as the sun is 
larger than Jupiter. But, neither Jupiter, nor any of the other three large 
planets, Saturn, Uranus and Neptune, is solidified like the earth and the 
other small planets. The large planets all appear to be composed mainly 
if not entirely of matter in the gaseous or vaporous state, although they 
are not hot enough to shine like the sun. We know but little about the 
actual conditions of any of the planets except the earth. 

The earth is about 8000 miles in diameter, and its surface, or 
“crust,” consists of rocks formed by the cooling and combination of 
chemical elements like those that exist in the form of incandescent gases 
and vapor in the sun. It was once thought that the interior of the earth, 
below a depth of a few hundred miles at the most, was in a molten state, 
on account of the fact that as we go deeper in the earth we find the tem¬ 
perature of the rocks increasing at the average rate of one degree for 
every 60 to 80 feet of descent. But at present it is doubted that any 
considerable quantity of molten rock exists in the earth. The phenomena 
of earthquake waves have proved that the globe, as a whole, must be at 
least as rigid as steel. This state of rigidity results from the enormous 
pressure, which amounts, by calculation, to 45,000,000 pounds per 
square inch at the earth’s center! 

The phenomena of hot springs and of volcanic eruptions simply 
show that, near the surface there may be “pockets” of molten material, 
while deeper the pressure is so great that all matter is held in a rigid state. 

The earth travels around the sun in a slightly elliptical orbit, at a 
mean distance of nearly 93,000,000 miles. As we have before said its 
distance in summer is about three million miles greater than its distance 
in winter. (In the southern hemisphere it is the reverse). It rotates on 
its axis from west to east, the same direction in which it goes around the 
sun, making 3631/4 turns in a year. The inclination of its axis has been 
dealt with elsewhere in this manual. 

The surface of the earth is covered to the extent of about seven- 
tenths with oceans, the remaining three-tenths consisting of land. 

The earth’s form is not exactly globular, but is that of an oblate 
spheroid, i. e. flattened slightly around the poles and bulged around the 
equator. The diameter through the equator is 7,926 miles and through 
the poles 7,900 miles. This form is believed to have been impressed by 
the centrifugal force of its rotation in the early period when it was yet 
so hot as to be in a plastic condition. The form is that which would be 
assumed by a plastic globe of the earth’s size rotating at about its present 
rate. 

Not only does the earth revolve around the sun, but together with 
the sun, and the whole system of planets, it travels in a northward direc¬ 
tion, nearly toward the bright star Vega, at a velocity of about 1 2 miles 


2S 




COSTELLO SOLAR DEMONSTRATING GLOBE 


per second, making more than 378,000,000 miles in a year that we are 
borne on through space in what, as far as appears, is virtually a straight 
course. If the other suns, the stars, also have planets, they are all making 
similar marvelous journeys, for there does not appear to be a star at rest 
anywhere in the universe. 


THE MAGNETIC POLES 

It is desirable that all pupils should clearly understand the difference 
between the poles of the earth s axis, or geographical poles, which are 
the true north and south poles, where all the meridians meet in a point 
at each end of the axis, and the magnetic north and south poles, whose 
locations are marked on the Globe, the north one being in North Amer¬ 
ica, near the eastern end of McClintock channel, on the coast of Boothia 
peninsula, about 20 degrees, say 1385 miles, south of the north geo¬ 
graphical pole; and the south one on the Antarctic continent, in Victoria 
Land, about 1 7 degrees 35 minutes, say 1220 miles, north of the south 
geographical pole The magnetic poles indicate the direction in which 
the compass needle points, and since that direction is northerly and 
southerly, the magnetic poles are very commonly confused with the geo¬ 
graphic poles The magnetic poles have nothing to do with any of the 
directions used in this manual. If you were at the north pole the mag¬ 
netic pole would be far south of you, while the pointing of the needle 
might give you a general notion of the direction in which the center of 
the United States lay: while if you were at the south pole the magnetic 

Zealand ^ ^ ^ y ° U th ® direction of Australia and New 


29 





COSTELLO SOLAR DEMONSTRATING GLOBE 


THE EQUATION OF TIME 

The measure of time for us is furnished by the rotation of the earth 
on its axis and its revolution around the sun. The first measures the 
length of the day; the second the length of the year. The sun serves as a 
clock-hand, apparently moving on the face of the sky, to show the rate 
of the earth’s two motions. 

Confining our attention first to the day by which, in this section, we 
always mean day and night, as one period, we find that although, taking 
the whole year round, it has a certain average, or mean, length, yet, in 
consequence of two causes which we shall briefly explain, it varies in 
length at different seasons. These variations are not due to any ir¬ 
regularity in the earth’s rotation, but to a combination of the effects of its 
rotation with those of its revolution around he sun and of the inclination 
of its axis of rotation from a perpendicular to the plane of its orbit. 

First fix in mind the fact that the length of the day as measured by 
the sun, (called the solar day, the one employed for all ordinary affairs), 
is equal to the time required by the sun to make one apparent revolution 
around the sky and come back again to the starting point, which is taken 
as the meridian, or noon line. Now, although the earth rotates at a reg¬ 
ular rate, (and there is a kind of day, which we shall describe later, that 
is based on this regularity of the earth s rotation), the sun, moving in the 
ecliptic, comes back to the meridian sometimes earlier and at other times 
,later, so that, evidently, its apparent motion is not regular. 

The first cause of this irregular motion of the sun is the eccentricity 
of the earth’s orbit, which causes the earth to change its distance from 
the sun by as much as three million miles, being nearest at Perihelion (in 
the beginning of January), and farthest at Aphelion (in the beginning of 
July). When it is nearer the sun the earth travels faster in its orbit and 
when it is farther from the sun it travels slower. Now, as we have before 
explained, the earth moving eastward around the sun causes the sun to 
appear to move eastward in the sky, and since the earth s rotation is also 
performed in an eastward direction, when it has made one complete turn 
with regard to space, or to the stars, which remain fixed in position, it has 
still to turn a little farther, and a little longer, in order to bring the meri¬ 
dian back under the sun, for the sun, too, has been moving eastward. 
The result is that when the earth’s speed in its orbit is greater than the 
average the sun’s apparent eastward motion is also more rapid, and, in 
consequence, the distance that the earth must turn to bring the sun back 
to the meridian is increased, and with it the length of the solar day. 

Accordingly, since the earth is nearest the sun at the beginning of 
January and farthest from the sun at the beginning of July, its speed is 
continually decreasing from January to July, and continually increasing 
from July back to January. But, as we have just seen, when the earth s 
orbital speed is increasing the relative length of the solar days is also in¬ 
creasing, while when the earth’s speed is decreasing the length of the days 
likewise decreases. The effect of the alternate increase and decrease ac- 


30 






COSTELLO SOLAR DEMONSTRATING GLOBE 


cumulates so that the solar days, as far as this cause is concerned, are 
longest about the 1st of January, or at Perihelion, and shortest near the 
1st of July, or at Aphelion. 

But there is another cause, operating simultaneously to alternately 
increase and decrease the length of the solar days. This is the obliquity 
of the ecliptic to the equator, resulting from the inclined position of the 
earth s axis of rotation. 

( U to the inclination of the sun s apparent path through the sky 

(t e ecliptic) with regard to the equator, the suns eastward motion is 
slowest at the equinoxes, where it crosses the equator at an angle of 23!^ 
degrees, and fastest at the solstices, where it attains its greatest distance 
from the equator, and for a while moves almost parallel with it. It fol- 
ows, then, that the obliquity of the ecliptic tends to make the solar days 
longest about the 1st of January, or at Prihelion, and shortens near the 
March 21st and Sept. 23rd (the equinoxes). 

But since these two causes of variation are acting simultaneously, 
while their effects do not coincide in time or in amount, we find them 
sometimes reinforcing and at other times counteracting one another. 

us in summer the retardation of the earth s speed as it retreats from 
the sun tends to shorten the day, but at the same time the increased east- 
ward movement of the sun near the solstice tends to lengthen the day, 
and the lengthening being greater than the shortening the final result is 
that in June and July the days are longer than the average. In winter 
the opposite case occurs, for then both causes combine to lengthen the 
ays. On the other hand, in spring and autumn both causes combine to 
shorten the days. In the end it comes out that the longest day of the 
.year occurs about Dec. 22, and the shortest about Sept. 1 7, and the 
greatest individual difference between them is 51 seconds, or about 
->/oths of a minute. Such difference, in itself, is too slight to be of im¬ 
portance in ordinary life, but the daily differences accumulate, now one 
way and now the other, for months in succession, so that at length their 
sum becomes noticeably great—and out of this arises the ‘ equation of 
time. 

It is now necessary to explain what is meant by “mean time" as 
contraste wit solar time. True solar time follows the variations in 
length of the solar days. It is indicated by a sun-dial, which marks noon 
only when the sun is truly on the meridian of the place where the dial 
stands. But it is impracticable to make a reliable clock capable of fol¬ 
lowing the vagaries of solar time, or keeping exact step with the sun. 
ror this reason true solar time cannot be used for ordinary purposes, be- 
cause we want our clocks to run regularly. But, advantage has been 
taken of the fact that, in the long run, taking in the whole year, the days 
have a certain average, or mean, length, and so a fictitious, or imaginary, 
sun has been invented which is assumed to move with perfect uniformity 
in the ecliptic, arriving at regular intervals of 24 hours on the meridian, 
or noon line. This is called the mean sun,” in contrast with the real or 
true sun, and clocks and watches are set to run to "mean time," i. e the 
time of the mean sun. 


31 






COSTELLO SOLAR DEMONSTRATING GLOBE 


But, although mean time serves excellently for ordinary affairs, 
nevertheless it is important for certain purposes to know how much mean 
solar time differs from true solar time. This difference is what is known 
as the equation of time. It is a correction which must be used in all 
exact observation of the times when astronomical phenomena occur. 

The equation of time represents for every day in the year the ac¬ 
cumulated gain or loss of the solar day with regard to its mean length, 
as it stands at that date. The daily figures for “apparent noon,” i. e. 
true solar noon, are published in the “American Ephemeris and Nautical 
Almanac.” Ordinary almanacs give them under the headings “sun 
fast, and “sun slow. The equation is geometrically represented by an 
annual curve, with two maxima, two minima, and four zero points. Ex¬ 
pressed in words, the most important features of the equation may be 
stated as follows: 

Four times a year, viz. April 15, June 14, Sept. 1, and Dec. 24, 
the sun and the clock are together, or solar time and mean time agree. 

Twice a year the sun attains a maximum advance on the clock “sun 
fast”), viz. May 14 and Nov. 2, the equation being 3 min. 48 seconds at 
the first of these dates, and 1 6 min. 20 sec. at the second. 

Twice a year the sun attains a maximum retardation with reference 
to the clock, (“sun slow”), viz. Feb. 1 1, and July 26, the equation 
amounting to 14 min. 25 sec. on the first, and 6 min. 20 sec. on the sec¬ 
ond of these dates. 

Owing to the periodical recurrence of leap year the dates vary 
slightly, but as given they are correct enough for general purposes. Exact 
figures for any date may be obtained from the Ephermeris. 

We will now illustrate the use of the equation of time. 

Observe that there are two ways in which the equation may be ap¬ 
plied, and both ways are used, according to the kind of time which is to 
be corrected. You may either correct the mean time (clock time) to 
obtain the apparent time (sun time), or you may correct the apparent 
time to obtain the mean time. In both cases the amount of the equation 
is added, but the addition is made algebraically, because the equation is 
marked plus ( + ), or minus (—), according as it lies on one side or the 
other of the line of average, and these signs are reversed if the time to 
which the correction is to be applied is interchanged. 

For instance, suppose that we wish to get the apparent time from 
the mean time, and suppose that the amount of the equation is 1 4 min. 
20 sec.: If the date falls in a part of the year when the solar days are 
longer than the average, the sun will be slow with reference to the clock, 
and the equation, if the Ephemeris is calculated for mean noon, will be 
marked—. Then, it being 12 hours 0 min. 0 sec., i. e., noon, by the 
clock, when we add the equation with the minus sign, we get 11 hr. 45 
m. 40 s. for the corresponding apparent time, which shows that, by the 
sun, the time is 14 m. 20 s. before noon; in other words the sun is slow 
to that extent. Or, let the date fall in a part of the year when the days 
are shorter than the average, and the sun is consequently fast by the 
clock. Say the equation is 16 m. 20 s. This will be marked H , in an 
Ephemeris based on mean noon, and when the addition is made we get 


32 



COSTELLO SOLAR DEMONSTRATING GLOBE 


12 hr. 16 m. 20 s. for the apparent time, showing that, by the sun, the 
time is 1 6 m. 20 s. after noon, or the sun is fast to that extent. 

But, if the correction is to be applied to the apparent time to get the 
corresponding mean time, at the same dates above given, then the 
algebraic signs must be interchanged. Then, in the first case, where the 
sun is slow, the equation wiil be marked + instead of —, and in the 
second case where the sun is fast, it will be marked — instead of +. If 
the pupil makes the additions with the signs changed, he will find that 
the result does not affect the real position of the sun with respect to the 
meridian, but shows it from the contrary points of view. A rule in a 
nutshell, avoiding the use of algebraic signs, would be: When the sun 
is fast the amount of the equation should be added to mean noon, or 
subtracted from apparent noon; when the sun is slow the amount of the 
equation should be subtracted from mean noon, or added to apparent 
noon. 

This comparison of the two methods of applying the equation has 
been made because much confusion of mind sometimes results from the 
fact that some text-books represent the curve drawn one way and some 
the other. Moreover, it will be found that the Greenwich solar tables are 
based on mean noon, and those of VFashington apparent noon, with cor¬ 
responding change of signs. 

It should be remarked that local mean time, with which we have 
been dealing, is not the time now usually kept by clocks and watches 
because these, for business reasons, are set to standard, or railroad time, 
which, when the locality is midway between two standard meridians 
throws the clock half an hour ahead or an equal amount behind, the true 
mean time. In addition to this, in many places, clocks and watches dur¬ 
ing a large part of each year, follow “daylight saving” time, which has 
the effect of throwing them an hour farther away from the true time. 

Inequalities of Forenoon and Afternoon 

There is an interesting effect produced by the equation of time upon 
the comparative length of forenoon and afternoon, which are assumed 
to divide the daylight period into two equal portions, one on each side 
of the meridian, or noon line. We habitually use mean, or clock, time 
to indicate noon, and although sunrise and sunset are referred to the 
real sun they are calculated in mean time. But, since the sun is at certain 
seasons ahead of the clock and at others behind it, the equation of time 
causes an inequality in the relative length of forenoon and afternoon, 
amounting to twice the equation, so that they are never of exactly the 
same length except on the four dates when the equation is zero. If the 
sun is ahead of the clock it crosses the meridian before mean noon and 
thus the length of the afternoon is relatively shortened. At the begin¬ 
ning of November this shortening amounts to about half an hour. But 
after Christmas the afternoon begins to get longer than the forenoon, 
attaining a maximum length near the middle of February. From the 
middle of April to the middle of June the forenoons are slightly the 
longer, from June 21 to Sept. 1st the afternoons again have the advant- 
age, but early in September the forenoons gain once more, attaining their 
maximum length in the beginning of November. 

33 



COSTELLO SOLAR DEMONSTRATING GLOBE 


Different Kinds of Day and of Year 

It may be added that the length of the day and the length of the 
year, the first depending on the rate of the earth’s rotation on its axis 
and the second on the speed of its revolution around the sun are, in 
themselves, practically invariable. The variations in the length of the 
day that we have been discussing affect only a particular kind of day, 
viz. the solar day, or day measured by the return of the sun to the noon 
line. This, which is the kind of day used for all ordinary purposes, de¬ 
pends, as we have seen, upon a combination of the effects of the earth’s 
revolution with those of its rotation. Because the revolution makes the 
sun advance in the sky in the same direction in which the rotation occurs, 
the earth has to turn a trifle longer each day in order to bring the sun 
back again to the noon line, than it would if the sun stood fast in the sky. 
Accordingly, the solar day does not accord with the true period of the 
earth’s rotation. 

But there is another kind of day, used by astronomers, which does 
accord with the true period of rotation. This is called the sidereal day. 
It is measured by the return to the meridian of a star; for the stars are so 
immensely far away that, unlike the sun, their position in the sky remains 
practically unchanged by the earth’s revolution. (There is a slight 
change, the annual parallax, but too insignificant to measureably affect 
the length of the day). However, although the sidereal day has the ad¬ 
vantage of indicating the true period of the earth’s rotation, it is unavail¬ 
able for use in the ordinary affairs of life because it does not accord with 
the apparent movements of the sun, upon which the phenomena of day 
and night, sunrise, sunset, etc., depend. Sidereal noon, which occurs 
when the Vernal Equinox, or First Point of Aries, among the stars, 
crosses the meridian, comes at some seasons in the daytime and at others 
in the night. This would never do for ordinary people, but it doesn t 
trouble the astronomer, who has in the observatory his sidereal clock, 
which tells him the hour by the stars,—and many a cool, delightful, 
stellar noon does he enjoy while the rest of mankind are asleep. 

The length of the sidereal day, measured in solar mean time, is 
about 23 hours, 36 minutes, 4 seconds, the length of the mean solar day 
being just 24 hours. Accordingly the solar day is about four minutes 
longer than the sidereal day, and in a year mean solar time gains one 
whole day upon sidereal time, so that there are 366]4 sidereal days in 
a year against 365 !4 solar days. A little reflection will show that this 
explains the apparent eastward revolution that the sun makes around the 
heavens, with respect to the stars once every year. It also explains why 
a given star rises, on the average, four minutes earlier each successive 
night. About March 22 every year sidereal noon and solar noon coin¬ 
cide. The sidereal time at solar mean noon for any day of the year is 
given in the Ephemeris. 


34 



COSTELLO SOLAR DEMONSTRATING GLOBE 


There are not only two but three kinds of year—the Sidereal Year, 
the Tropical Year, and the Anomalistic Year. The first is measured by 
the time taken by the sun in making one apparent revolution around the 
heavens with respect to a fixed star. Its length is 365 days, 6 hours, 9 
minutes, 9 seconds of mean solar time. The second kind of year, the 
Tropical Year, is measured by the time taken by the sun to make one 
a pparent revolution with respect to the Vernal Equinox. This is the year 
on which chronology and the calendar are based. Its length in mean 
solar time is 365 days, 5 hours, 48 minutes, 45J/2 seconds. The third 
kind of year, the Anomalistic, is measured by the time that the sun takes 
to pass from Perihelion to Perihelion, and its length is 365 days, 6 hours, 

1 3 minutes, 48 seconds. It has practically no interest except to astrono¬ 
mers. 


35 



COSTELLO SOLAR DEMONSTRATING GLOBE 


THE STANDARD TIME ZONES 

The Standard Time System, on which railroad schedules are based, 
together with practically the whole chronology of business and industry 
as well as of social life, presents one of the most striking evidences of the 
rapidity of movement that characterizes all human affairs in our day. 
Until well toward the close of the Nineteenth Century transportation on 
land had not become rapid enough to introduce any serious complica¬ 
tion by its relation to the speed of the earth s axial rotation, or the index 
of that rotation furnished by the sun s daily westward progress through 
the sky. 

But in the early eighties it became evident that the growing speed 
of railroad travel, and the increasing complexity of time schedules cov¬ 
ering the whole width of a continent, imperatively demanded a general 
readjustment of the time shown by clocks and watches to that indicated 
by the movements of the mean sun, which is the fundamental time-keeper 
for the entire earth. The result was the adoption, in 1883, by general 
agreement among the American railroads, of a system of standard time, 
based on the meridians of longitude in such a way that all places included 
within certain bounding meridians should have the same time without re¬ 
gard to local differences arising from their being situated, some a few de¬ 
grees farther west, and others a few degrees farther east. In the same 
year, an international conference held at Washington discussed and ap¬ 
proved the plan, together with suggestions looking to the world-wide 
adoption of a universal time standard based on the meridian of Green¬ 
wich as the common origin. 

Put into a few words, the principle of the system is as follows. 
Starting from the meridian of Greenwich and counting westward around 
the earth, (which is the way of the sun), every 1 5 degrees of advance in 
longitude corresponds to one hour of time, because there are 360 degrees 
in the circumference of the earth, and the sun, taking 24 hours to go once 
around, must go 1 5 degrees, or one 24th of 360 degrees in one hour. 

Accordingly, when the sun is on the noon line at Greenwich it 
must be one hour east, or short, of the noon line at a place 1 3 degrees 
west of Greenwich; two hours short at a place 30 degrees west, and so 
on In other words, noon (or any other chosen hour) arrives one hour 
later for every 1 3 degrees that the place of observation is farther west. 
So, as the observer travels westward, his watch, unless continually reset, 
steadily gains time on, or gets more and more ahead of, the local time¬ 
pieces keeping the time of the places through which he passes. 

To prove this it is not necessary to start from Greenwich, for the 

principle holds all around the world. 

For instance, suppose you start from Chicago any day at noon, and 
travel directly west. When you have gone 1 3 degrees, which carries 
you into western Nebraska, your watch marks noon when the sun is still 
an hour short of the noon line, and when the local clocks mark A. 
And if you go another 1 5 degrees, into southeastern Oregon, your watch 



COSTELLO SOLAR DEMONSTRATING GLOBE 



37 





































































































COSTELLO SOLAR DEMONSTRATING GLOBE 


will mark noon two hours ahead of the local timepieces (if they are set 
to true local time). 

If you traveled eastward instead of westward the effect would be 
reversed. 

Starting at noon from Chicago, and carrying local Chicago time, 
when you arrived at the Connecticut river, you would have gone 15 
degrees eastward, or 1 5 degrees to meet the sun, and your watch would 
be slow by local time, because it would mark noon an hour after the 
sun had crossed the noon line. 

Now, in the days when men in general stayed pretty close to their 
homes, and when transportation and travel were mostly confined to short 
distances and brief periods, no great disadvantage was felt from discrep¬ 
ancies of time arising from differences of longitude, because in those days 
such discrepancies were not large. But, as we have already remarked, 
the case assumed a very different aspect as soon as fast railroad trains 
began to transport people as far as from New York to Chicago between 
suppertime and breakfast. That meant an hour difference of time pro¬ 
duced during a night s sleep. 

In fact, it is not possible to get rid of these time differences—the 
best that we can do is to regulate and systematize them. It would not be 
possible to keep a watch, or a clock, or a time schedule, in absolute and 
instantaneous accord with the changing local time as an observer moves 
east or west, for the sun does not suddenly leap from one 1 5-degree 
longitude line to the next at the beginning or the end of every hour, but 
it continually advances in step with the rotation of the earth, so that 
even in the short time of four minutes it moves one degree westward. 

However, a degree of longitude on the earth’s surface, within the 
regions where the population is greatest, is between 50 and 60 miles long, 
and a difference of time of only four minutes, or even of several times 
four minutes, is not a very serious matter, provided that its effects are 
guarded against in cases where they do become of importance. Such 
provision is made by the Standard Time system. 

In the Standard Time system, as applied in this country, four meri¬ 
dians of longitude, separated by interspaces of 1 5 degrees, are taken as 
the central lines, or axes, of four successive time zones, each one hour, or 
1 5 degrees, broad, while together they cover the whole width of the 
United States from the Atlantic to the Pacific. Each zone theoretically 
extends 7'/2 degrees on each side of its central meridian, or axis. All 
places included in one of these four zones have the same standard time, 
which is the time of the central meridian of that particular zone. This, 
of course, does not affect the local time of such places, that time con¬ 
tinuing to be governed by the relative situation in longitude. But, for 
nearly all purposes of everyday life, the local time is disregarded and 
clocks and watches in every part of a given zone are set to the time of 
its standard meridian. Places just on that meridian have identity of local 
and standard time. 

But since the zones extend l/i degrees on each side of their cen¬ 
tral lines, the local time of a place situated near one of the borders of 


38 



COSTELLO SOLAR DEMONSTRATING GLOBE 


any zone differs half-an-hour from the time of the central jneridian. 
This is, theoretically, the greatest amount by which the local time of any 
place can differ from the standard time of its zone, but two places sit¬ 
uated on the opposite borders of a zone differ a whole hour in their local 
time. 

In passing from one zone to the next, the time changes by just one 
hour, the clock being set back if the passage is from east to west, and 
ahead if from west to east. This may be better understood if we refer 
to the accompanying chart. There it will be seen that the first of the 
four zones covers the Atlantic coast states, beginning at the north-eastern 
corner of Maine. Its central, or standard meridian, is the 75th meridian 
west of Greenwich, which crosses the country a little west of New York, 
and very close to Philadelphia. The time of that meridian is five hours 
slow on Greenwich, i. e. when it is noon at Greenwich it is 7 A. M. of 
the same day on the 75 th meridian. This is called Eastern Standard 
time. 

Now, the whole of the New England states and Middle states, and 
a large part of the Southern states, are included in the 75 th meridian 
zone, a space hundreds of miles wide, and within which the local times 
may differ by a whole hour; yet under the Standard Time system, their 
watches and clocks all keep together, so that there is no need to change 
the setting of your watch until you pass across the western border of the 
zone, which crosses the Great Lakes, and runs near Detroit, Columbus, 
and Atlanta. When you cross that border going west, you set your watch 
just one hour back. 

Then you have the time of Chicago and the Middle West, called 
Central Standard time, whose meridian is the 90th, or six hours slow on 
Greenwich. And this you keep unchanged until you cross into the zone 
of Mountain Standard time, whose central meridian is the 105th, while 
its time is seven hours slow on Greenwich. The fourth of the zones, on 
entering which from the east you set your watch back another hour, is 
that of Pacific Standard time, centered on the 120th meridian, eight 
hours slow on Greenwich. But, except to show the common origin of the 
system from a world view-point, there is no need to refer back to Green¬ 
wich, the time of the Eastern, or 75 th meridian, zone serving for a start¬ 
ing point. 

We have seen that if a place is on the eastern border of its zone, 
l/l degrees from the central line, its local time is half an hour fast by 
the central standard, while if it is on the western border its local time is 
half an hour slow. But now consider the situation of things with regard 
to two places just facing one another, and virtually in contact, one being 
on the western and the other on the eastern border of its own zone. 
Their local time would be practically the same, but by Standard time 
they would be one hour apart, just as if they were actually separated by 
15 degrees of longitude, or a distance of about 750 miles. 

Such cases as this may serve to illustrate the origin of the zig-zag 
shape of the border lines between the zones as shown in the chart. 
While the central line of each zone is strictly coincident with the corres- 


39 



COSTELLO SOLAR DEMONSTRATING GLOBE 


ponding meridian of longitude, whose time fixes the standard for the 
whole zone, the border lines do not, as they theoretically should do, 
follow meridians but are very crooked, swerving sometimes east and then 
again west, as sinuous in their course as rivers. A large part of the 
western border of the Central zone is thrown beyond the 1 00th meridian, 
which puts it more than 1 0 degrees, instead of 7 / 2 degrees from its cen¬ 
tral meridian, the 90th. 

These variations are due to efforts of the Interstate Commerce 
Commission to adjust conflicting interests and wishes of the inhabitants 
of the regions traversed by the boundaries. According to information 
furnished by the Superintendent of the U. S. Naval Observatory the chief 
reasons determining the courses of the boundary lines, which have many 
times been modified, while at the start no attempt seems to have been 
made to keep the zones exactly 15 degrees wide, are as follows: 

(a) Grouping of railroads and other commercial routes into divi¬ 
sions or sections having the same time; for example, variation of the 
boundary line to include a terminal or important center in the same 
division, or area, as the larger part of the roadway. 

(b) Unifying the time system of certain areas having natural boun¬ 
daries, such as rivers, lakes, mountains, etc. 

(c) Generally avoiding divisions of counties, townships, and cities. 

(d) Passing the boundary lines generally through the less densely 
populated areas, and avoiding division of more densely populated com¬ 
munities. 

(e) Satisfying the demands of the people of certain areas and sec¬ 
tions near the boundaries of the zones by giving them local benefits or 
advantages. 

It may be added that, although it is not shown, except a little cor¬ 
ner, on the United States chart, there is another zone, used in Canada, 
and known as the Intercolonial, whose central meridian is the 60th, four 
hours from Greenwich, while it includes Newfoundland, Nova Scotia, 
New Brunswick, and a part of Quebec within its area. 


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